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SOME EFFECTS OF POTASSIUM SALTS 
ON SOILS 



A THESIS 

PRESENTED TO THE FACULTY OF THE GRADUATE SCHOOL 
OF CORNELL UNIVERSITY FOR THE DEGREE OF 

DOCTOR OF PHILOSOPHY 



BY 



RAYMOND STRATTON SMITH 



SEPTEMBER, 1918 



Reprinted from Memoir 35. June, 1920, of Cornell University Agricultural 
Experiment Station. 



SOME EFFECTS OF POTASSIUM SALTS 
ON SOILS 



A THESIS 

I'RE.SENTtD TO THE FACULTY OF THE GRADUATE SCHOOL 
OF CORNELL UNIVERSITY FOR THE DEGREE OF 

DOCTOR OF PHILOSOPHY 



ii\ 



RAYMOND 5TRATTON SMITH 



5EPTF.MBER, 1918 



Reprinted from Memoir iS, June, 1920. of Cornell University Agricultural 
F-Xperlment Station. 



! LiBnARY Or C<JNGni:';S 1 



?i/l/\R26l921 



i OOCbii 



o ,:>w.>;>tO''-' \ 






^' CONTENTS 

PAGK 

Historical review 57.1 

Effect of potassium and manganese salts on plant growth 571 

Potassium salts 571 

Manganese salts 573 

Effect of potassiimi and manganese salts on nitrifi(;ation in soils . . . 574 

Potassium salts 574 

Manganese salts 576 

Effect of reaction of the soil on nitrification 578 

Interchange of leases 579 

Conclusions 580 

Experimental work 581 

Soils used 581 

Preparation of the soils 581 

Plan of the experimental work 582 

Experimental methods 584 

Pot cultures 584 

Soil extract cult urcs 584 

Nitrification 584 

Soil acidity determination 585 

Experimental results 585 

Pot cultures 585 

Soil extract cultures 587 

Nitrification 590 

Interchange of bases 595 

Summary 599 

Literature cited 602 



567 



SOME EFFECTS OF POTASSIUM SALTS ON SOILS 



SOME EFFECTS OF POTASSIUM SALTS ON SOILS 
R. S. Smith 

The factors that determine the abihty of a soil to support plant growth 
are known to be very complex, and any modification of this ability 
brought about by materials added to the soil is at least equally complex. 
It is now generally recognized that the secondary effects of fertilizing 
materials which are added to a soil may ultimately prove either beneficial 
or injurious when measured in terms of crop yields. The deleterious 
effects of ammonium sulfate have been particularly noted. The secondary 
effects of other fertilizer salts have l)een less thoroly studied because 
their action is thought to be less pronounced. However, attention has 
been called to various effects exerted by other materials, including the 
salts of potassium. The somewhat conflicting experimental data bearing 
on the effects of the chloride and the sulfate of potassium on the soil as 
a medium for plant growth led to the work reported in this paper. 

The method of attacking the prolilem was, first, to determine the effect 
of various applications of potassium chloride and potassium sulfate on 
the growth of wheat, both in the variously treated soils and in water 
extracts of the soils; and secondly, to attempt to get at the causes of the. 
effect of these salts on crop growth as noted in this work and as noted 
by other investigators. 

HISTORICAL REVIEW 

EFFECT OF POTASSIUM AND MANGANESE SALTS ON PLANT GROWTH 

Potassium salts 

The stimulative action on the growth of the higher plants exerted by 
the salts of potassium which are commonly used as fertilizing materials, 
is recognized. That this action is in part secondary seems evident from 
the fact that the specific effects noted vai-y with different soils and with 
the same soil variously treated. 

Ordinarily, these salts would probably not be used in sufficient quantity 
to prove directly harmful to plant growth; but under certain intensive 
systems of farming, in which heavy applications of fertilizers are made, 

571 



572 R. S. Smith 

such a result might follow. Lyon, Fippin, and Buckman (1915) make 
the statement that "it [potassium] may be present in large quantities 
in the soil and yet exert no harmful effect on the crop." Whether this 
statement refers to soluble salts of potassium added to the soil, or to the 
slowly soluble compoiuids in the soil minerals, is not stated. There is a 
possibility, however, that even the ordinary applications of potassium 
salts may result in an increased loss from tlic soil of other bases, particu- 
larly calcium. 

But little work has been done to determine at what concentration the 
salts of potassium become toxic to plant growth in soils. Headden 
(1915) found that yellow-berry in wheat is increased by the application 
of 150 pounds of potassium to the acre. He ascribes this condition to 
the excess of solul)le potassium over soluble nitrogen. This effect of a 
comparatively small application of a potassium salt in aggravating an 
abnormal condition in the wheat crop is of interest in this connection in 
that it indicates a significant modification of the soil as a medium for 
plant growth. 

Harris (1915), from an extensive investigation of the effect of alkali 
salts on the germination and growth of seedlings in three different soils, 
reports the concentrations of potassium chloride and potassium sulfate 
at which these salts become harmful to wheat seedlings. He found that 
heavier applications of these salts were required to cause injury to the 
seedlings than would ever be applied, even in the most intensive systems 
of farming. 

McCool (1913) determined the effect of the chlorides of ammonium, 
magnesium, potassium, and calcium on the germination of pea seeds in 
soil. The salts were harmful in the order given. Potassium chloride 
caused slight injury when used at the rate of about 7456 pounds in 
2,000,000 pounds of soil. The character of the soil is not stated by the 
writer. 

Voelcker (1909), in conducting pot experiments with wheat at the 
Woburn experiment station, in which the chloride, the sulfate, the car- 
bonate, and the nitrate of potassium were used in such amounts as to 
supply the soil in each case with 0.0075 per cent of the metal potassium — 
which is equivalent to 166 pounds of the chloride, 312 pounds of the 
sulfate, 248 pounds of the carbonate, and 369 pounds of the nitrate, per 
2,000,000 pounds of soil — noted injury with the carbonate. It is difficult 



Some Effects of Potassium Salts on Soils 573 

to understand how such small apphcations of any of these salts could 
cause injury to wheat. 

Much work has been done on the toxicity of bases in solution cultures 
with various crop plants. This phase of the study is typified by the 
investigations of McCool (1913) on a large number of bases, including 
potassium. This type of investigation, however, has little direct sig- 
nificance in soil studies, because the conclusions drawn cannot be applied 
with a soil medium due to side reactions which are involved when so 
complex a medium is employed. McCool found that the chlorides of 
barium, manganese, ammonium, magnesium, sodium, potassium, and 
calcium were toxic to pea seedlings in the order named. It is of interest 
to note that manganese stands near the head of the list. 

The degree of toxicity of all the salts is much less in soil than in nutrient 
solution. As has been noted, McCool found that potassium chloride 
caused slight injury to the germination of pea seeds in soil when applied 
at the rate of about 7456 pounds to 2,000,000 pounds of soil, and Harris 
reports much higher concentrations than this as l)eing necessary to produce 
a toxic condition except in the case of coarse sand. 

It thus appears that injury to plant growth has been found to result 
from the use of potassium salts in large quantities; that applications at 
the ordinary rate have been found to cause injury in but one case; and 
that small applications may possibly accentuate pathological conditions 
in the growing plant. 

No reports of experiments on the growth of seedlings in soil extract 
made from soils to which only potash salts had been added, have been 
found in the literature. 

Abbott, Conner, and Smalley (1913) report some soil-extract-culture 
experiments with corn, using soil high in solul^le aluminium salts. This 
work is of interest in this connection in that it agrees with the con- 
clusions of other investigators that the water extract from unproductive 
field soils is toxic to the root growth of seedlings. 

Manganese salts 
Manganese, as is noted later in this paper, is one of the bases replaced 
by potassium in some soils, and, since it has been shown by some investi- 
gators to have considerable influence on plant growth, a brief review 
of the literature regarding its action is here given. 



574 R. S. Smith 

As sliown by Skinnor and Sullivan (1914), manganese increases the 
oxiclizinjr power of plant roots. This, however, was not accompanied 
by increased growth when the plants were grown i-n fertile soil. Infertile 
soils seemed to respond to manganese when it was used in small quantities, 
varjang from 5 to 50 parts of manganese to 1,000,000 parts of soil. 

Experiments by Skinner and Reid (1916) on silty clay loam of an acid 
nature; at Arlington, Virginia, in which manganese sulfate was applied 
annually at the rate of 50 pounds to the acre previous to planting, show 
a decrease in the yield of wheat and cowpeas and inconsistent results 
with rye. When the lime requirement of the soil was just satisfied, the 
depression was decreased; and when an excess of lime was used, the crop 
yields were increased by manganese, except in the case of potatoes. 

The results of other workers agree in the main in showing that the salts 
of manganese increase the yields of field crops when used in small quanti- 
ties. In some instances a decrease results, and the work of Skinner and 
Reid seems to indicate that the reaction of the soil is an important factor. 

Little work has been done to determine at what concentrations salts 
of manganese become toxic to plant growth in soils. McCool (1913), 
using a sandy loam soil, found that manganese chloride in solution was 
toxic to peas when added at the rate of 380 cubic centimeters of N/50 
solution to 1000 grams of soil. This rate of application is equivalent to 
about 181 parts of the element manganese to 1,000,000 parts of soil. 
McCool found also that calcium overcame this injurious action, while 
Kelley (1908) reports that lime had no such effect. 

The conclusion seems justified that if a neutral salt when added to 
the soil replaces even small amounts of manganese, the presence of this 
replaced base may affect crop growth adversely or occasionally beneficially, 
depending on other factors not well understood. 

Other bases replaced by various fertilizer treatments are known to 
be toxic to plant growth, particularly iron and aluminium. But since 
neither of these elements was found to be present in the water extracts 
of the soils used in this work, no discussion of their action seems necessary. 

EFFECT OF POTASSIUM AND MANGANESE SAI.TS ON NITRIFICATION IN SOILS 

Potassium salts 
Potassium salts have been found to protluce specific effects on nitrifica- 
tion. Under certain conditions a stimulation has been noted, while under 



Some Effects of Potassium Salts on Soils 575 

other conditions the reverse has been the case. The Hterature has been 
searched in an attempt to discover what effects potassium salts have 
on nitrification, and any specific effects that have been found to accompany 
certain conditions resulting from the application of potassium salts to 
soils. A close correlation between the nitrifying power of a soil and its 
crop-producing power may not exist, but the two are likely to be associated. 
A study of the nitrifying power of a soil should, then, furnish some 
indication of its crop-producing power and help to explain any departures 
from the normal in crop growth. 

Dumont and Crocbetelle (1893) report favorable effects of potassium 
salts on nitrification in soils rich in organic matter and limestone. They 
later (1894) report work with a sandy humous soil stated to be poor in 
lime. This soil as reported contained 17.5 per cent of humus and 0.285 
per cent of limestone. Potassium carbonate and potassium sulfate, both 
with and without lime, were used in different amounts. Potassium 
carbonate was used in increasing amounts from 0.1 to 6 grams, to 100 
grams of soil. Marked stimulation was found to accompany its use 
up to 4.5 grams, and then there was a steady decrease in the nitric nitrogen 
found. Potassium sulfate without lime had no consistent effect. The 
character of the results indicates that the differences found in the latter 
treatments were due to factors other than those under study. When 
2.5 grams of limestone were applied in addition to the potassium sulfate, 
there was a constant increase in the amount of nitric nitrogen found 
with an increase in the amount of potassium sulfate used, the heaviest 
application being 5 grams to 100 grams of soil. 

Lyon and Bizzell (1918) report the nitrogen recovered from the lysimeter 
tanks at Cornell University. Apparently potassium sulfate without 
lime depressed nitrification. Lime counteracted this effect, but even 
with lime the sulfate did not cause any appreciable stimulation of the 
process. 

Greaves (1916), in laboratory experiments on the effect of potassium 
salts on the bacterial activities of sedimentary soils derived from limestone 
and quartzite, found that potassium chloride and potassium sulfate used 
at the rate of from 6.1 to 8602 parts per million depressed nitrification 
at all con(;cntrations. Potassium nitrate and potassium carbonate, used 
at the same rates, stimulated nitrification at the lower concentrations 
but became toxic at the higher, the nitrate at 48.9 parts per million and 



o7G 11. S. Smith 

the carbonate at 3910 parts per million. Greaves concluded that the 
extent of stimulation is governed largely by the cation, and that the 
toxicity of potassium salts is governed by the electro-negative ion com- 
bined with the potassium, since he found that the chlorides of sodium, 
magnesium, manganese, and iron, and the sulfates of calcium and manga- 
nese, increased bacterial activity, while the chlorides of potassium and 
calcium and the sulfates of sodium and potassium failed to cause any 
stimulation. 

Pichard (1884) found that potassium sulfate caused strong nitrification 
of the organic nitrogen in a soil high in organic matter, but that its influ- 
ence was not so marked as was that of calcium sulfate or sodium sulfate. 

Allen and Bonazzi (1915) studied nitrification in soil samples from 
the plots at the Ohio experiment station. Anmionium sulfate in solution 
was used as the nitrifiable material at the rate of 21.2 milligrams of 
nitrogen per 100 grams of soil. The samples were incubated for ten days. 
The results with the samples from the potassium sulfate plots — which 
had received 80 pounds of the salt to the acre on corn, oats, and wheat 
of the five-years rotation — failed to show any increase in nitrification 
over the check ; in fact, denitrification apparently took place in some cases. 

Peck (1911) found that potassium sulfate used at the rate of 0.5 gram 
in 500 grams of sugar-cane soil decreased the bacterial activity, as measured 
by bacterial numbers and nitrogen fixation during one month of incubation. 

Renault (1910) cites experiments by Dumont which show that slow 
ammonification and subsequent nitrification is always accompanied by 
a low percentage of potash. 

It thus appears that potassium fertilizers, when applied at the usual 
rate under field conditions, commonly exert a depressing influence on 
nitrification. Under laboratory conditions both the chloride and the 
sulfate of potassium have generally been found to exert a depressing 
effect on nitrification, even when used in amounts as smaU as 12 pounds 
to 2,000,000 pounds of soil. Lime apparently counteracts the injurious 
effects of small applications of the sulfate and permits some stunulation of 
the process of nitrification. 

Manganese salts 

Salts of manganese are known to have marked influence on nitrification, 
and since manganese, as has already been stated, is one of the soil bases 



Some Effects ok Potassium Salts on Soils 577 

replaced ])y potassium, it is of importance in this connection to note what 
its effects have been found to be. 

Kelley (1912), working with Hawaiian soils, found that those high in 
manganese had a stronger nitrifying power than those low in this element. 
However, the soils high in manganese were in a better physical condition, 
and their higher nitrifying power was attributed to this fact rather than 
to any difference in manganese content. 

Montanari (1914) found that manganese dioxide and manganese car- 
bonate apparently stimulated nitrification, while the sulfate exerted less 
stimulation or even depressed the process. 

Leoncini (1914) found that manganese dioxide increased nitrification 
when used in amounts as high as 2.2 per cent, but that heavier applications 
apparently had no influence. 

Brown and Minges (1916) determined the effect of various manganese 
compounds on nitrification and ammonification in Carrington clay loam. 
In the ammonification tests dried blood was used, and in the nitrification 
trials ammonium sulfate was used. Manganese chloride apparently had 
no effect on nitrification in amounts less than 0.5 per cent; but from that 
point on, increasingly heavy apphcations caused increased depression, 
until, with 5 per cent of the salt, nitrification was inhibited. With 
manganese sulfate there was decisive depression of nitrification when 
0.5 per cent of the salt was used, but with increasingly heavy applications 
the results did not show an increasing depression. Manganese nitrate 
apparently depressed nitrification, the magnitude of depression inci'easing 
with the amount of the salt used. Manganous oxide in most cases 
depressed nitrification, altho definite conclusions regarding this point 
cannot be drawn from the data presented. 

Greaves (1916) found the chloride, the sulfate, and the nitrate of 
manganese toxic to ammonification in soil at concentrations of 68.6, 
137.3, and 274.6 parts of added manganese, respectively, to 1,000,000 
parts of soil. The carbonate of manganese was without effect even at 
the highest concentration used, 6045.6 parts per million. 

Olaru (1915) reports three experiments on nitrogen fixation in nutrient 
solutions with varying amounts of manganese. He found that stimulation 
of the process resulted from all the concentrations of manganese used, 
but that the proportion of 1 part of manganese to 200,000 parts of 
solution gave the greatest stinmlation. Olaru suggests that increases in 



578 R. S. Smith 

crop yioUls which have been found to follow the use of fertilizing materials 
are clue, not only to the direct action of the materials on the plants, but 
also to their modification of the bacterial activities of the soil. 

There appears to be much conflict in the data cited regarding the effect 
of manganese compounds on nitrification. In some cases very low con- 
centrations of the various salts proved to be toxic, while in others relatively 
high concentrations were stimulative. Too little information is given 
regarding the nature of the soil used in the various experiments to permit 
any attempt to account for the discrepancies. 

EFFECT OF REACTION OF THE SOIL ON NITRIFICATION 

The reaction of the soil is generally considered to be an important 
factor in determining its capacity to support a vigorous nitrifying flora. 
Brown (1911:55) apparently takes an extreme position when he says: 
" The effect of lime on nitrification and the necessity for the presence 
of lime in the soil for the process to occur, have long been a matter of 
common knowledge." 

The literature bearing on this problem is voluminous and no attempt 
is made here to summarize it. The stimulating action of lime on nitrifi- 
cation is generally conceded, but apparently the process may go on 
in soils very deficient in lime. 

Fred and Graul (1916) state that " it seems that under laboratory 
conditions, the beneficial effect of calcium carbonate on plant growth 
must be accounted for by some processes other than the direct effect on 
nitrification." Temple (1914) and White (1914) report vigorous nitrifica- 
tion in strongly acid soils. 

In the work herein reported, the heaviest treatments with the chloride 
and the sulfate of potassium caused a slight increase in the lime require- 
ment of the soils, but in no case was the increase more than 300 pounds 
of calcium carbonate to 2,000,000 povmds of soil. This small difference 
in reaction is not considered significant so far as nitrification is concerned, 
particularly in view of the fact that nitrification has been shown to proceed 
in strongly acid soils. The increasing depression in nitrification which 
will be shown to have accompanied increasingly heavy applications of 
the potassium salts must be accounted for on some basis other than 
increased acidity. 



Some Effects of Potassium Salts on Soils 579 

interchange of bases 

As stated by Sullivan (1907), the fact that water is purified by filtration 
thru sand was known in the time of Aristotle. That common salt can 
be removed from water by filtering the water thru sand or soil has likewise 
been known for many years. Hilgard (1911 : 267) states that the latter 
is a clearly physical effect. When neutral salt solutions are filtered thru 
soil, the filtrate may be either acid or alkaline, depending on whether 
the cation or the anion of the salt has been removed the more strongly. 
This phenomenon has been attributed to selective ion adsorption. Truog 
(1916) and Sullivan (1907) think that it is better accounted for by an 
exchange of bases, in which iho base of the soluble salt interchanges in 
part with the iron or the aluminium of the soil. The salts of the latter 
metals hydrolyze strongly in dilute solution and give an acid value. 

The fact that soils enter into a chemical exchange with salt solutions 
was recognized at an early date by Thompson (1850), who found that 
an ammonium sulfate solution filtered thru soil gave up its ammonium 
in exchange for calcium. Way (1850, 1852, 1854), in a number of experi- 
ments, extended the observations of Thompson and found that the 
nitrates, the chlorides, and the sulfates of ammonium, potassium, sodium, 
and magnesium, when filtered thru soil, exchanged their bases for calcium 
from the soil. Way concluded that the active constituent of the soil 
entering into this interchange was a hydrated alumino-silicate of the clay 
fraction. It is now thought that any silicate is capable of entering into 
these reactions, according to Sullivan (1907). 

Peters (1860) found that the absorption of the cation of a salt in neutral 
solution was of about the same magnitude regardless of the form of com- 
bination. Thus, he found that potassium was absorbed in about equal 
amount from equivalent solutions of i<s chloride, its sulfate, and its 
carbonate. In an extensive investigation Klillenberg (1867) confirmed 
Peters' conclusion. He found that the base entered into the reaction 
in about the same amount, whether it was combined with the sulfate, 
the nitrate, or the chloride. 

The bases are mutually replacable, but are not replaced with equal 
facility. The stability of the silicate or the alumino-silicate is the con- 
trolling factor. Lemberg (1870, a and b, 1872, 1876), in a series of studies, 
found that the sodium in silicates is replaced more readily by potassium 



580 . R. S. Smith 

than is potassium ])y sodium, and tliat magnesium is replaced less readily 
from its silicate by calcium than is calcium by magnesium. 

\im Bemmolen (1878) treated a soil with a solution of potassium 
chloride, and found that the potassium had been exchanged for sodium, 
calcium, and magnesium. Van Bemmelen states that the absorption of 
the entire salt takes place very slightly if at all. 

The important point l)rought out by Van Bemmelen in this early work 
and reemphasized by him later (Van Bemmelen, 1900), is that colloidal 
silica and silicates do not abstract and concentrate the salts from neutral 
salt solutions when filtered thru soils. Any such apparent effect is due, 
he believes, to a redistribution of the salt in the solution between the 
water of the colloid and the water of the solution. 

Joly (1902-04), Briggs and Lapham (1902), and Dittrich in 1903 (cited 
by Sullivan, 1907:26) also have presented data tending to show that the 
action of neutral salt solutions on soils consists in an equivalent exchange 
of bases. 

Ruprecht and Morse (1917) report the presence of soluble salts of iron, 
aluminium, and manganese in soils repeatedly dressed with ammonium 
sulfate without the addition of lime. 

It thus appears that neutral salts of potassium when added to the soil 
are strongly absorbed, thus resulting in the liberation of other bases which 
may have either beneficial or harmful effects on plant growth. These 
effects may be due to some direct effect of the replaced bases on the 
plant's activities, or they may be induced indirectly by the modification 
of some of the soil's properties. 

COXCLUSIONS 

It appears from this summary of the literature that the common 
fertilizer salts of potassium have usually been found to exert harmful 
effects on plant growth only when used in large quantities. These effects 
may be accounted for in part by basic exchange, in which case the com- 
position of the soil would ])e an important factor. Significant modifications 
of the l)acterial activities in the soil may be another factor. In the 
following pages are Reported the results of experimental work which was 
designed to throw fight on these problems. 



Some Effects of Potassium Salts on Soils 581 

EXPERIMENTAL WORK 
SOILS USED 

Three soils were used in the experiments here reported — Hagerstown 
silt loam, Dekalb silt loam, and Volusia silt loam. 

Hagerstown silt loam is a residual soil derived from limestone. It is 
known as a productive soil, and has good surface drainage and good 
underdrainage. The sample was collected near State College, Penn- 
sylvania, from an old field which had never been fertilized in so far as 
could be learned. In collecting the soil the immediate surface was scraped 
off and the soil was taken to a depth of eight inches. 

Dekalb silt loam is a residual soil derived from sandstone and shale. 
Its productivity is considered as poor to medium. It is typically poorl}^ 
underdrained. The sample was collected from an abandoned field near 
Snow Shoe, Pennsylvania, in the same manner as was the Hagerstown 
silt loam. 

Volusia silt loam is a glacial soil composed of a small proportion of 
glacial material mixed with soil material derived from local sandstone 
and shale. There is such a wide variation in this soil that it cannot 
be characterized as a series. The sample was collected near Ithaca, 
New York, from an unproductive, poorly underdrained field, the same 
method being used as was used in collecting the other soils. 

PREPARATION OF THE SOILS 

The soil samples were brought to the laboratory and immediately 
screened thru a 4-millimeter screen. Small samples of the screened soils 
were taken for moisture and acidity determinations, and pots were filled 
with a known weight of the soil calculated to the water-free basis. After 
the pots were filled, the contents of each pot were emptied on an oilcloth, 
the required quantity of precipitated calcium carbonate and potassium 
salt was added and thoroly mixed with the soil, and the pot was refilled. 
In the case of the Volusia soil, the potassium salt was added in solution 
after the calcium carbonate had been mixed with the soil and the pot 
had been refilled. The pots were then brought to weight with distilled 
water. Sufficient calcium carbonate was added to the Hagerstown and 
Dekalb soils to just satisfy their lime requirement, which amounted to 
2 tons of calcium carbonate to 2,000,000 pounds of soil in each case. 



582 



R. S. Smith 



With the Volusia soil varying amounts of the carbonate were used, as 
follows: Series 1 — no lime, lime requirement 3393 pounds of calcium 
carbonate to 2,000,000 pounds of soil; Series H' — lime requirement just 
satisfied; Series III — 2 tons of calcium carbonate to 2,000,000 pounds 
of soil in excess of the lime requirement. 

PLAN OF THE EXPERIMENTAL WORK 

On the Hagerstown and Dekalb soils no crop was grown the first year. 
Composite samples of each treatment, in triplicate, were taken for nitrate 
determinations, with a |-inch brass tube, the day after bringing the pots 
to weight and at regular intervals thereafter during the first year. The 
moisture content was maintained at approximately 24 per cent (water- 
iree basis) by bringing the pots to weight weekly with distilled water. 



TABLE 1. Treatments of Hagerstown and Dekalb Silt Loam Soils 
(Lime requirement of soils just satisfied; moisture content maintained at 24 per cent) 



Pot 


Pounds of potassium salt to 
2,000,000 pounds of soil 




KCl 


K2SO4 


a 
1 . K 




200 

500 

1,000 

2,000 

3,000 




200 

500 

1,000 

2,000 


fa^ 

O . K 


C J 

3/^1 


IcJ 

al 
4. h\ 


. c. 

KJh 


UJ 

Jt] 


.cJ 


3,000 



Some Effects of Potassium Salts on Soils 



583 



The following year the triplicates were thoroly mixed on oilcloth, duplicate 
pots were filled with each treatment, and wheat was planted and grown 
to maturity thru the winter and spring. At the time of making up the 
duplicate pots, samples were taken, air-dried, and stored to be used later 
in determining the effect of treatment on water-soluble bases and on the 
growth of wheat seedlings in the water extracts of the soils. 

TABLE 2. Treatments of Volusia Silt Loam 
(Moisture content maintained at 30 per cent) 

Series 1 — No CaCOa; lime requirement 3393 pounds CaCOa to 2,000,000 
pounds of soil 



Pot 



1 
2 
3 
4 
5 



Pounds of KCl 

to 2,000,000 

pounds of 

soil 



Number of pots 





200 

500 

1,000 

2.000 



Cropped to 
wheat 

4 1 -gallon 
4 1 -gallon 
4 1 -gallon 
4 1 -gallon 
4 1 -gallon 



No crop 
grown 

3-gallon 
3-gallon 
3-gallon 
3-gallon 
3-gallon 



Series II — Same plan as Series I, with lime requirement just satisfied 

Series III — Same plan as Series I, with 4000 pounds of CaCOa to 2,000,000 
pounds of soil in excess of lime requirement 



In the case of the Volusia soil, quadruplicate 1-gallon pots were made 
up of each treatment, to be cropped to wheat, and one 3-gallon pot in 
each treatment was filled to be used later in the other studies. All of 
these pots were brought to weight weekly (30 per cent moisture content, 
water-free basis) with distilled water. All of the laboratory determina- 
tions, including soil extract cultures with wheat seedlings, were made on 
samples from the 3-gallon pots, which had been kept in the greenhouse 
imder the same conditions as the cropped pots and maintained at an 
approximately constant moisture content for about seven months. 

The outline given in tables 1 and 2 makes the plan of the work clear. 



584 II. S. Smith 

EXPERIMENTAL METHODS 

Pot cultures 

Two-gallon pots were used with the Ilagerstown and Dekalb soils, 
each pot containing the equivalent of 9j pounds of water-free soil. One- 
gallon pots were used with the Volusia soil, each pot containing the 
equivalent of 6 pounds of water-free soil. Duplicate pots were used 
with the Hagerstown and Dekalb soils, and quadruplicate pots with the 
Volusia soil. The Hagerstown and Dekalb soils were maintained at a 
moisture content of 2-^ per cent, water-free basis, and the Volusia soil 
at 30 per cent. These moisture contents gave approximately two-thirds 
saturation. 

Soil extract cultures 

Soil extract. — The soil extract for the solution cultures and the analyses 
for water-soluble bases was prepared by adding five parts of water to 
one part of soil (after correcting for the water already in the soil), shaking 
for three hours, and hnmediately filtering thru Pasteur-Chamberland 
filters. 

Analysis of extract. — The official methods of analysis of the United 
States Bureau of Chemistry' were used, with the following exceptions: 

Manganese was determined by the ammonium persulfate method as 
described by Hillebrand (1910). Calcium was precipitated according to 
the official method, and titrated with potassium permanganate after 
solution in dilute sulfuric acid. 

Soil extract cultures. — - The soil extract cultures were run in duplicate. 
Erlenmeyer flasks of 500 cubic centimeters capacity were used for culture 
vess(>ls. Four wheat plants were grown in each flask by using a paraf- 
fin (h1 paper cover thru which four holes were punched to receive the 
rootlets. The plants were allowed to grow for four weeks. They were 
then removed, photographs were taken of the roots, and the dry weights 
were determined. 

Nitrification 

In th(> nitrification trials, tumblers were used for containers and 100 
grains of soil was placed in each tumbler. Three nitrifiable materials — 
ammonium sulfate, ammonium hydroxide, and dried l)lood — were used. 



•Official and provisinnal methods of analysis, Association of Official Agricultural Chemists. U. S. Bur. 
Chum., Bui. 107. 1912. 



Some Effects of Potassium Salts on Soils 585 

The ammonium sulfate and the ammonium hydroxide were appHed in dikite 
sohition, and the dried blood was well mixed with the soil on a piece 
of oilcloth. The cultures were incubated at room temperature and were 
brought to weight every six days with distilled water. Excessive evapora- 
tion was prevented by covering the tumblers with a layer of cotton placed 
between pieces of cheesecloth. The period of incubation, percentage 
of moisture maintained, and nitrifiable material used, are shown with 
each table in which the results are given. 

Nitrates were determined by the phenoldisulphonic-acid jnethod as 
described by Schreiner and Failyer (190G). 

Soil acidity determination 

The lime requirement of the soils was determined by a modified Veitch 
method (White, 1914). 

EXPERIMENTAL RESULTS 

Pot cultures 
The crop on the Hagerstown and Dekalb soils was attacked by sparrows 
on the afternoon of the day before it had been intended to harvest the 
pots, and as a result only the yield of straw is given. In the case of the 
Volusia soil, the probable error of the average for the quadruplicate pots 
is so high as to render most of the possible comparisons of questiona])le 
value. The probable errors were computed by means of Peter's formula 
as given by Mellor (1909), 

-( + v) 

R = ± 0.8453 - , 

n v^i-1 

in which - (+ v) denotes the sum of the deviations of each observation 
from the mean, disregarding their sign, and n denotes the number of 
observations made. 

The results of the pot experiments are given in tables 3 and 4. 

Potassium sulfate increased the yield of straw over the check in both 
the Hagerstown and the D(4vall) soil. In the Plagerstown soil there was 
a continued increase in yield with an increase in the rate of application 
after 500 pounds was reached. In the case of the Dekalb soil the data 
are not conclusive, except that, as witli the Hagerstown soil, there is no 
evidence of a toxic condition with any of the treatments. 



586 



R. S. Smith 



TABLE 3. Yield of Wheat Straw in Pot Cultures with Hagerstown and Dekalb 

Silt Loams 

(Lime requirement of soils just satisfied) 



Pot 



Pounds of 
K.SO, to 

2,60(),0()() 
pounds 
of soil 



Yield of straw 
in grams 



Duplicates 



Average 



Pounds of 
KCl to 

2,000,000 
pounds 
of soil 



Yield of straw 
in grams 



Duplicates 



Average 



1 

2 
3 
4 
5 
6 

1 

2 
3 
4 
5 
6 





200 

500 

1,000 

2,000 

3,000 



200 

500 

1,000 

2,000 



3,000 



Hagerstown silt loam 

4.36 
4.25 
5.56 
5.26 
5.02 
5.15 
6.70 
4.85 
6.50 
5.65 
6.69 
16.16 



Dekalb silt loam 

/1. 85 
1.87 
1.82' 
1.92 
1.85 
1.8S 
1.59 
1.71 
2.08 
l.SS 
2.01 
2.10 



4.31 


5.41 


5.09 


5.77 


S.08 


6.43 





86 




87 




86 




65 




98 


2 


06 





200 

500 

1,000 

2,000 

3,000 





200 

500 

1,000 

2,000 

3,000 



4.12\ 

4.18 ■ 

4.45 

4.37 

4.87 

4.07 

3.91 

3.95 

3.86 

4.02 

3.11 

3.41 




4.15 
4.41 
4.47 
3.93 
3.94 
3.26 



1.95 
1.91 
1.79 
1.94 
1.68 
1.68 



Potassium chloride apparently became toxic at the lOOO-poiind treat- 
ment with the Hagerstown soil and at the 200()-pound treatment with 
the Dekalb soil. The data, however, are not conclusive, and warrant 
only tentative conclusions regardino; the rate of application necessary 
to bring aI)out a toxic condition in these soils. 



Some Effects of Potassium Salts on Soils 



587 



TABLE 4. Yield of Wheat Straw and Grain in Pot Cultures with Volusia Silt 

Loam 



Series 


Pounds of 
KCl to 

2,000,000 
pounds 
of soil 


Straw 

(average of 

quadruplicates, 

in grams) 


Grain 

(average of 

quadruplicates, 

in grams) 


I 

No lime; lime requirement 3393 pounds 

CaCOa to 2,000,000 pounds of soil 




200 

500 

1,000 

2,000 


6.3±0.41 
6.5±0.45 
6.6 ±0.40 
6.7±0.14 
8.6±0.44 


3 03 ±0.10 
3. 14 ±0.18 
3.17±0.13 
3.22±0.13 
3.85 ±0.19 


II 
Lime requirement just satisfied 




200 

500 

1,000 

2,000 


8.8 ±0.85 
7.2±0.37 
6.6 ±0.23 
7.4±0 13 

7.9 ±0.13 


4 09 ±0.62 
3:46 ±0.30 

2 79 ±0.13 

3 12 ±0.12 
3.59 ±0.05 


III 

4000 pounds CaCO,, to 2,000,000 pounds 
of soil in excess of lime requirement 




200 

500 

1,000 

2.000 


12.1 ±0.76 

13.4 ±0.53 
10.7 ±0.22 

15.5 ±2.45 
11.9 ±0 33 


6.06 ±0.68 

5. 13 ±0.66 
2.80 ±0.44 
5.18 ±0.64 

4.14 ±0.12 



Soil extract cultures 

Both the root and the top growth of the wheat seedhngs were very 
uniform in the duphcate water extract cuhures. The dry weights, how- 
ever, while uniform between duphcates, did not give a good measure 
of the comparative root growth betweeii cultures, and consequently are 
not reported. 

The presence of some toxic substance or substances in certain of the 
cultures is indicated in figures 161 to 163. The sensitiveness of the roots 
of seedlings to toxic substances has been adequately demonstrated by 
Schreiner and his associates in the United States Bureau of Soils, and by 
Breazeale and LeClerc, of the Laboratory of Plant Physiology of the 
United States Department of Agriculture. 

In the extract from the Hagerstown soil (fig. 161) the chloride is seen 
to have stimulated root growth thruout the series, the greatest degree 
of stimulation resulting from the 500-pound treatment. In the sulfate 
series there is seen a progressive stimulation of root growth up to the 



588 



R. S. Smith 




Fig. 161. root growth of wheat seedlings in water extracts from hagerstown silt 
loam which had received varymg amounts of the chloride and the sulfate of 
potassium 




Fig. 102. root growth (jf wheat seedlings in water extracts from dekalb silt loam 

WHICH HAD received VARYING AMOUNTS OF THE CHLORIDE AND THE SULFATE OF POTAS- 
' SIUM 



Some Effects of Potassium Salts on Soils 



589 



2000-pound treatment, and a marked toxicity with the 3000-pound treat- 
ment. These latter results agree in the main with the yield of straw in 
the pot cultm-es except in the case of the heaviest sulfate treatment. 
In this case the extract cultures showed strong toxicity, while no such 
condition was present in the pot cultures. 

In the extract from the Dekalb soil (fig. 162) no distinct toxicity was 
shown in any of the cultures when compared to the checks. The checks, 
however, were apparently toxic. With the chloride the 200-pound treat- 



^PL 



jpa^ ipi 



^^^S^^^^Em^^^S 



jraH! mi 



^.^ffl_4Un--JrPi- 









JEEBSL 



Ml ' r 



Fig. 163. root growth of wheat seedlings in water extracts from volusia silt loam 

WHICH HAD received VARYING AMOUNTS OF POTASSIUM CHLORIDE, BOTH WITH AND WITH- 
. OUT LIME 

ment caused the greatest stimulation of root growth, while with the 
sulfate there was little difference between the degree of stimulation in 
the 200- and the 500-pound treatments. These results are not reflected 
in the yields from the pot cultures. The yields from the pots were very 
small and the final weights are probably not a good index of the relative 
vigor of growth. 

In the Volusia extract cultures (fig. 163) the important point l)rought 
out is the neutralization of the toxic condition by the calcium carbonate. 



590 



R. S. Smith 



A distinctly toxic condition was evident in the no-lime scries with the 
heavier chloride treatments. This condition was less pronounced in the 
series receiving enough lime to just meet the lime requirement of the soil, 
and almost entirely disappeared when 4000 pounds of lime to 2,000,000 
pounds of soil in excess of the lime requirement of the soil was used. 

Nitrification 

As a measure of the activity of the nitrifying organisms in the variously 
treated soils, determinations were made of the nitrates accumulated over 
long periods of time and of the nitrification of added materials. The 
accumulation of nitrates in the three soils used is shown in tables 5, 6, 
and 7, respectively. The figures represent the milligrams of nitrate 
nitrogen in 100 grams of soil as determined when the pots were set up 
and at stated intervals thereafter. The difference between the initial 
nitrate content and that after a given interval represents the actual 



TABLE 5. 



Accumulation op Nitrates in Hagerstown Silt Loam as Determined 
AT Intervals after the Experiment Was Set U^p 





(Moisture content, 24 per 


cent) 








Pounds of potassium salt 
to 2,000,000 pounds of soil 


Rlilligrams of nitrogen as nitrates in 100 
grams of soil 




At time 
of setting 
up experi- 
ment 


After 
33 days 


After 
61 days 


After 
86 days 





(KCl) 


1.90 

2.12 

1.66 

1.50 

Trace 

1.41 


2.50 
1.86 
1.80 
1.94 
2.09 
2.04 


3.33 
3.07 
2.91 

2.82 
3.02 
3.26 


3.10 


200 


2.86 


500 


3.05 


1,000 


2.94 


2,000 


2.82 


3,000 


2.83 






0. 


(K.SO4) 


1.53 
1.96 
1.68 
1.69 
2.15 
1.46 


2.06 
2.53 
2.83 
2.61 
2.53 
2.54 


3.88 
3.22 
3.65 
3.89 
3.81 
3.97 


3.87 


200 


3.60 


500 

1,000 


3.35 
4.06 


2,000 


4.40 


3,000 


4.48 







Some Effects of Potassium Salts on Soils 



591 



accumulation, or, in some cases, loss. In the case of the Volusia soil, 
nitrate accumulation was determined but once, after a seven-months 
period. 



TABLE 6. 



Accumulation op Nitrates in Dekalb Silt Loam as Determined at 
Intervals after the Experiment Was Set Up 





(Moistu 


re content, 24 per 


cent) 








Pounds of potassium salt 
to 2,000,000 pounds of soil 




Milligrams of nitrogen as nitrates in 100 
grams of soil 




At time 
of setting 
up experi- 
ment 


After 
33 days 


After 
61 days 


After 
86 days 


0. 


(KCl) 




Trace 
Trace 
Trace 
Trace 
Trace 
Trace 


0.65 
0.40 
0.49 
0.68 
0.36 
Trace 


1.14 

0.92 

1.04- 

0.91 

0,60 

0.49 


1 69 


200 


1 36 


500 


1 56 


1,000 

2,000 


1.44 
1 27 


3,000 


69 









(K0SO4) 




Trace 
Trace 
Trace 
Trace 
Trace 
Trace 


0.71 
0.70 
0.67 
0.89 
0.81 
0.63 


1.44 
1.31 
1.65 
1.86 
2.13 
1.87 


1 25 


200 

500 


1.97 

2.27 


1,000 


2.71 


2,000 


2.16 


3,000. ... 


2.08 







It will be noted that in every case the potassium chloride decreased 
the accumulation of nitrates, and that the depression increased regularly 
with an inci'ease in the amount of chloride applied except for one or 
two minor exceptions. In the Volusia soil the degree of depression with 
the heavy chloride treatments was less in the lime series than in the 
no-lime series, indicating the tendency of the lime to overcome the harm- 
ful effects of the potassium chloride. 

Potassium sulfate seems to have exerted a stimulating effect on nitrate 
accumulation. In the Dekalb soil the greatest degree of stimulation 
occurs with the 1000-pound treatment, and then there is a gradual decline 
with the two heavier treatments. 



592 



II. S. Smith 



TABLE 7. Accumulation of Nitrates in Volusia Silt Loam after Seven Months 

(Moisture content, 30 per cent) 





Pounds of 

KCl to 

2,000,000 

pounds of 

soil 


Milligrams of nitrogen 

as nitrates in 100 

grams of soil 


Series 


At time 
of setting 
up experi- 
ment 


After 

seven 

months 


1 

No lime; lime rcciuirement 3393 pounds CaCOs 

to 2,000,000 pounds of soil 




200 

500 

1,000 

2,000 


2.00 
2.00 
2.00 
2.00 
2.00 


6.06 
5.55 
4.88 
3.77 
2.32 


II 

Lime requirement just satisfied 




200 

500 

1,000 

2,000 


2.00 
2.00 
2.00 
2.00 
2.00 


7.50 
7.14 
5.97 
4.81 
4.08 


III 

4000 pounds CaCOs to 2,000,000 pounds of soil in 

excess of lime requirement 




200 

500 

1,000 

2,000 


2.00 
2.00 
2.00 
2.00 
2.00 


9.76 
9.09 
8.69 
7.01 
6.45 



With the twenty-one-days incubation period (tables 8 to 10), all of 
the soils in which the lime recjuirenient was just satisfied show the 
initial depression of nitrification with the 1000-pound treatment of 
the chloride. When ammonium hydroxide was the nitrifiable material 
added (table 10), altho the initial (h^pression occurred at this point the 
nitrates found in the heaviest chloride treatment exceeded those in the 
ciieck, indicating perhaps some action due to the basic nature of the 
hydroxide. 

In the Hagerstown soil treated with potassium sulfate (table 8), 
nitrification was depressed slightly b(^low that in the check with the 
heaviest sulfate treatment. This was not the case in the Dekalb soil 
(table !)), altho in the latter soil the 8000-poimd treatment caused less 
stimulation of the jirocess than did the 2000-pound treatment. 



Some Effects of Potassium Salts on Soils 



593 



TABLE 8. Nitrification in Hagerstown Silt Loam When Ammonium Sulfate Is 

Used 

(Moisture content, 24 per cent; incubation period, 21 days) 





Nitrogen as nitrates in 100 


Nitrogen in (NH4)2S04 




grams 


of soil 


nitrified 


Pounds of potassium salt 










to 2,000,000 pounds 




21.2 milli- 






of soil 


Chock 


grams N 


Milligrams 


Per cent 




(milligrams) 


added 










(milligrams) 






(KCl) 













3.11 


13.98 


10.87 


51 27 


200 


2. SO 


14.42 


11.56 


54.52 


500 


3.05 


14 93 


11.88 


56.03 


1,000 


2.94 


12.95 


10 01 


47 21 


2,000 


2. 82 


10 94 


8.12 


38.30 


3,000 


2.83 


8 . 28 


5 45 


25 70 






(K2SO4) 













3.87 


17.18 


13.31 


62.31 


200 


3.60 


16.80 


13.20 


62.26 


500 


3.35 


17.52 


14.17 


66.83 


1,000 


4.06 


19.03 


14.97 


70.61 


2,000 


4.40 


21.60 


17.20 


81 . 13 


3,000 


4.48 


17.64 


13 16 


62 07 







TABLE 9. Nitrification in Dekalb Silt Loam When Ammonium Sulfate Ls I'sed 
(Moisture content, 24 per cent; incubation period, 21 days) 



Pounds of potassium salt 

to 2,000,000 pounds 

of soil 



Nitrogen as nitrates in 100 



grams of soil 



Check 
(milligrams) 



21.2 milli- 
grams N 
added 
(milligrams) 



Nitrogen in (NH4)2S04 
nitrified 



Milligrams 



Per cent 



(KCl) 
....... . 

200 

500 

1,000 

2,000 

3,000 

(K2SO4) 



200 

500 

1,000 

2,000 

3,000 



1.69 
1.36 
1.56 
1.44 
1 27 
0.67 



3.49 
4.28 
3.61 
2.21 
1.21 



1.76 
2.13 
2.72 
2.17 
0.94 
0.52 



1.25 
1.97 
2.27 
2.71 
2.16 
2 OS 



3.62 
3.58 
4.76 
5.55 
5 74 
4.82 



2.37 
1.61 
2.49 
2.84 
3.58 
2.74 



8.30 

10.04 

12.83 

10.23 

4 43 

2 45 



11 17 
7.59 

11 74 
13 39 
16.88 

12 92 



594 



R. S. Smith 



The beneficial action of lime is again brought out in table 10. Here 
it is shown that in the no-limc scries depression in the nitrification of 
ammonium hydroxide accompanied the application of potassium chloride. 
Wlien the lime requironKMit of the soil was just satisfied, the initial 
depression occurred with the 1000-pound treatment, and when lime was 
used in excess of the lime requirement the initial depression occurred with 
the 2000-pound treatment'. 

TABLE 10. Nitrification in Volusia Silt Loam When Ammonium Hydroxide Is 

Used 
(Moisture content, 30 per cent; incubation period, 21 days) 







Nitrogen as nitrates in 


Nitrogen i 


n NH4OH 






100 grams of soil 


nitrified 




Pounds 
of KCl to 




















Series 


2,000,000 




21.2 milli- 








pounds 


Check 


grams N 


MilU- 


Per 




of soil 


(milli- 
grams) 


added 
(milli- 
grams) 


grams 


cent 


I 





6.05 


8.19 


1.94 


4.7.3 


No lime: lime requirement .3.393 


200 


5.88 


7.41 


1.53 


3.73 


pounds of CaCOa to 2,000,000 


500 


4.88 


6.25 


1.37 


3.34 


pounds of soil 


1,000 


4.54 


6.00 


1.46 


3.56 




2,000 


2.70 


3.50 


0.80 


1.95 







7.09 


11.11 


3.42 


SM 


II 


200 


5.58 


10.96 


5.38 


13.12 


Lime requirement just satisfied 


500 
1,000 


5. 33 
5.12 


12.50 
10.77 


7.17 
5.65 


17.48 
13.78 




2,000 


3.33 


7.41 


4.08 


9.95 


III 





11.11 


17.02 


5.91 


14.41 


200 


11.11 


20.00 


8.89 


21.68 


4000 pounds of CaCOs to 


500 


9.20 


20.00 


10.80 


26.34 


2,000,000 pounds of soil in 


1,000 


8.00 


19.52 


11.52 


28.10 


e.xcess of lime requirement 


2,000 


7.41 


16.02 


8.61 


21.00 



The results from the use of dried blood as the nitrifiable material are 
given in table 11. Here again the beneficial action of lime in counteracting 
the ill effects of potassium chloride is shown very strongly. It is possible 
that a longer incubation period would have allowed more nitrification 
in Series I. An acid condition is apparently very unfavorable to the 
nitrification of dried blood. 



Some Effects of Potassium Salts on S<jils 



505 



TABLE 11. NiTHiFicATioN IN Volusia Silt Loam When Dried Blood Is Used 
(Moisture content, 30 per cent; incubation period, 14 days) 





Pound.s 

of KC! to 

2,000,000 

pounds 

of soil 


Nitrogen as nitrates in 
100 grams of soil 


Nitrogen in blood 
nitrified 


Series 


Check 
(milli- 
grams) 


21.2 milli- 
grams N 
added 
(milli- 
grams) 


Milli- 
grams 


Per 
cent 


I 
No lime; lime requirement 3303 
pounds of CaCOs to 2,000,000 
pounds of soil 




200 

500 

1,000 

2,000 


7.69 
7.76 
6.25 
4.54 
3.57 


7.84 
7.14 
5.88 
4.66 
3.17 


0.15 
00 
00 
012 
00 


0.71 
00 
00 
0.57 
0.00 


II 

Lime requirement just satisfied 




200 

500 

1,000 

2,000 


8.60 
S.OO 
7.41 
5.63 
4.60 


10 96 
10.00 

8 . 69 
7.47 
5.06 


2. 36 
2.00 
1.28 
1.84 
0.46 


11.23 
9 52 
6.09 
8.76 
2.19 


III 

4000 pounds of CaCOs to 
2,000,000 pounds of soil in 
excess of lime requirement 




200 

500 

1,000 

2,000 


11.59 

11.11 

9.63 

8.42 

7.76 


21.54 
21.87 
20.58 
18.64 
16.08 


9.95 
10.76 
10.95 
10.22 

8.32 


47.38 
51.28 
52.14 
48.66 
39.51 



Another series was run with Vohisia soil, using ammonium hydroxide 
and incubating for fourteen days. The results of this series are not 
included herein, for they simply confirm the results of the twenty-one- 
days incubation period. 

In the foregoing discussion of the nitrifying power of the variously 
treated soils, it has been assumed that the increase in nitrates during 
the incubation period was due entirely to the oxidation of the added 
materials. This assiunption is clearly not entirely justified, and yet any 
other method of oljtaining the desired information would probably be 
open to equally serious criticism. 

Jnlerchangc of bases 
The marked influence of potassium chloride on the nitrate bacteria 
raised the cjuestion as to whether the toxic effect might be due to replaced 



59() 



R. S. Smith 



bases. With this possibihty in view, tlie water extracts of the variously 
treated soils were tested for calcium, iron, aluminium, magnesium, and 
manganese, and when found to be present each of these elements was 
determined quantitatively. 

No iron nor aluminium was found in any of the extracts, and no 
manganese nor magnesium was found in certain of them, as appears in 
tables 12 to 15. All determinations were made in duplicate, and 
checked very closely, so that only the averages are given. 

TABLE 12. Amounts of Calcium in Variously Treated Soils 





Parts of calcium per million parts of soil extract 


Pounds of potassium 
salt to 2,000,000 


Hagerstown 


Dekalb 


Volusia 


pounds of soil 


Lime 

requirement 

just 

satisfied 


Lime 

requirement 

just 

satisfied 


No lime; 
lime require- 
ment 3393 
lbs. CaCOs 


Lime 

requirement 

just 

satisfied 


Lime 4000 

lbs. in 

excess of 

requirement 


(KCi) 



21.6 
30.5 
34. S 
44.2 
60.3 
72.2 


2.9 
5.7 
6.1 
6.5 
11.6 
13.0 


15.1 
15.9 
23.2 
26.5 
38.4 


27.7 
26.7 
28.5 
44.8 
51.4 


33 6 


200 


40 7 


500 


46.2 


1,000 


54.3 


2,000 

3,000 


53.7 








^ 


(K2SO4) 



21.1 
24.1 

25.2 
29.5 
36.7 
45.1 


2.1 
3.8 
3.8 
4.5 
5.5 
6.0 








200 








500 








1,000 








2,000 








3,000 


















As shown in table 12, with equal (but not equivalent) weights of the 
chloride and the sulfate of potassium the chloride replaced more calcium 
than did the sulfate. This result is to be expected, since equal weights 
of the two salts do not carry equal weights of the base. 

As has been noted, Peters (1860) and Kiillenberg (18(57) both found 
that tiu! Ixise entered into the reaction independently of its form of com- 
bination. It does not follow from this, however, that equivalent weights 



Some Effects of Potassium Salts on Soils 



597 



of the bases in a soil would appear in (he extracts from the same soil 
treated with various acids of the same base, because of the different 
solubilities of the products of the reactions. Calcium sulfate is less 
soluble than calcium chloride, and consequently less calcium would 
probably be found in the extract of a soil treated with the sulfate than 
in one treated with the chloride of potassium. This is apparently the 
condition that existed in these soils, for there is less calcium present in 
the extracts from the sulfate treatments than should be present theoretically 
if the relative solubilities are discarded and only the replacing power of 
the potassium actually added is considered. 

No magnesium was found in any of the extracts from the Volusia 
soil. This series is reported by Robinson (1914) to be low in magne- 
sium. In the Hagerstown and Dekalb soils (table 13), less magnesium 
than calcium was replaced by potassium. This result is in accord with 
results from previous work. 

TABLE 13. Amounts of Magnesium in Variously Treated Soils 





Parts of magnesium per million 
parts of soil extract 


Pounds of potassium salt to 2,000,000 pounds of soil 


Hagerstown 


Dekalb 




Lime 

requirement 

just 

satisfied 


Lime 

requirement 

just 

satisfied 


(KCl) 



15.6 
18.0 
19.4 
21.2 
24.8 
26.2 


2.9 


200 


3 5 


,500 


3.7 


1,000 


3.7 


2,000 


5.0 


3,000 


5.7 






(K2SO4) 



12.8 
15.0 
15.8 
16.8 
18 
1!) 6 


2.5 


200 . 


2.5 


500 


2.5 


1 000 


2 2 


2,000 


2.7 


3,000 


2.8 







598 



R. S. Smith 



That appreciable amounts of manganese went into solution in the 
Hagerstown and Dekalb soils is indicatcHi in table 14. As previously 
notiMl. manganese has been found to be strongly toxic both to plant growth 
and to nitrification. Skinner and Reid (1916), as already stated, found 



TABLE 14. Amounts of Manganese in Variously Treated Soils 





Parts of manganese per million parts of soil extract 


Pounds of potassium 
salt to 2,000,000 


Hagerstown 


Dekall) 


Volusia 


pounds of soil 


Lime 

requirement 

just 

satisfied 


Lime 

requirement 

just 

satisfied 


No lime; 
lime require- 
ment 3393 
lbs. CaCOa 


Lime 

requirement 

just 

satisfied 


Lime 4000 

lbs. in 

excess of 

requirement 


(KCI) 



24 
0.47 
0..57 
0.71 
1.15 
1.64 


0.7s 
1.11 
1.92 
3.12 
4.17 
6.25 


0.00 

0.00 

Trace 

0.30 

0.65 


00 
00 
0.00 
0.00 
Trace 


0.00 


200 


00 


rm 


0.00 


1,000 


0.00 


2,000 


0.00 


3,000 












(K2S04) 




0.93 
0.99 
1.44 
2.03 
2.35 
2. SO 


0.50 
0.53 
0.S3 
l.OS 

1.7.S 
2.. 50 








200 








rm .... 








1,000 








2,000 








3,000 

















that manganese chloride was distinctly harmful to crop growth in an 
acid soil when used at the rate of 50 pounds to the acre. This application 
would be equivalent to about 14 parts of manganese to 1,000,000 parts 
of soil if it is assumed that the salt became mixed with the surface soil 
only. The Dekalb soil showed approximately this concentration of 
manganese when its extract became toxic to wheat seedlings. To bring 
this out more clearly, the parts per million of manganese in dry soil are 
calculated in table 15. 

The presence of manganes(^, however, cannot be considered as a com- 
plete explanation for the toxic condition found in the extract cultures 



Some Effects of Potassium Salts on Soils 



599 



and indicated in the pot cultures, and for the depression of nitrification 
particularly with the chloride treatments. The extract from th(\ Volusia 
soil was toxic to wheat seedlings in certain treatments and no manganese 
was found in solution. Toxicity in solution cultures may arise from a 

TABLE 1.5. Amount of Manganese in Dry Roil 



Pounds"of potassium salt to 2,000,000 pounds of soil 



Parts per million of water-soluble 
manganese in dry soil 



Hagerstown 



Lime 

requirement 

just 

satisfied 



Dekalb 



Lime 
requirement 

just 
satisfied 



(KCl) 



200 

.500 

1,000 

2,000 

3,000 

(K0SO4) 



200 

500 

1,000 

2,000 

3,000 



1.20 
2.35 
2.85 
3.55 
5.75 
8.20 



3.90 

5. 55 

9.60 

15.60 

20 85 

31 25 



0.93 
0.99 
1.44 
2.03 
2.35 
2.80 



50 
65 
65 
42 
92 
50 



number of conditions, one of which is a lack of balance of nutrients. It 
is of interest, nevertheless, tho perhaps not of significance, to note that 
the soil having the highest content of water-soluble manganese showetl 
the weakest nitrifying power and the smallest accumulation of nitrates, 
as well as the smallest growth of wheat in pot cultures and of wheat roots 
in extract cultures. 

SUMMARY 

Three silt loam soils were used in the experiments rc^portcMl licrcin, 
each soil being representative of a large area in the United States. The 
productivity of the soils ranged from high to very low. 



600 R. S. Smith 

The soils were screened and the pots were filled with the treated soils 
as described. The official methods of analysis of the United States 
Bureau of Chemistry w(n-(^ used, with the exceptions noted. 

Potassium sulfate increased the yield of straw in Hagerstown soil and 
showed no toxic effect in Dekalb soil. Potassium chloride apparently 
became toxic to wheat in Ha^erstown soil with the lOOO-pound application; 
in the Dekalb soil tiieie was a slight decrease in yield with the 2000-pound 
treatment. 

In the extracts from the Hagerstown soil, potassium chloride stimulated 
the root gi'owth of wheat seedlings at all concentrations, the greatest 
stimulation occurring with the 500-pound treatment. With the sulfate 
there was a progressive stimulation to the 2000-pound treatment, and 
a marked toxicity with the 3000-pound treatment. In the extracts from 
the Dekalb soil the checks were toxic to the root growth of wheat seedlings. 
With the chloride the 200-pound treatment caused the greatest stimulation, 
and there was a decrease in stimulation and apparent toxicity with the 
heavier treatments. With the sulfate the 500-pound treatment caused 
the greatest stimulation, and there was a decrease in stimulation and 
apparent toxicity with the heavier treatments. In the extracts from 
the no-lime series of the Volusia soil, toxicity to root growth became 
evident with the 500-pound treatment. Lime overcame the toxicity even 
with the heaviest chloride treatment. 

Potassium chloride decreased the accumulation of nitrates in all cases. 
Lime overcame this effect in part. Potassium sulfate apparently stimu- 
lated the accumulation of nitrates in Hagerstown and Dekalb soils. 

The heavier potassium chloride treatments depressed nitrification of 
added materials. Potassium sulfate stimulated the process in all three 
soils with the exception of the heaviest treatment with Hagerstown soil. 
Lime had a tendency to correct the depression of the chloride in the 
Volusia soil, but did not entirely overcome it. 

No iron nor aluminiinn was found in any of the water extracts, and no 
manganese was found in the extracts from the Volusia soil; hence the 
harmful action of the potassium salts cannot be attributed to replaced 
iron or aluminium, or to manganese in the case of Volusia soil. Both 
the chloride and the sulfate of potassium replaced calcium strongly. Less 
calcium appeared in the extract from the sulfate-treated series than 
would be expected, possibly because of the relative insolubility of calcium 



Some Effects of Potassium Salts on Soils 601 

sulfate. Magnesium was replaced less strongly than was calcium. 
Manganese was replaced in very appreciable amounts in Hagerstown and 
Dekalb soil, particularly in the latter. The soil highest in water-soluble 
manganese showed the least nitrifying efficiency, the smallest growth 
of wheat in pot cultures, and the poorest growth of wheat rootlets in 
extract cultures. 

The effects of potassium salts on plant growth are due to a complex 
interaction of factors, involving perhaps the direct action of the salts 
on plant growth and on bacterial activities, and also the action of bases 
replaced by the potassium, particularly manganese. 



602 R. S. Smith 



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Some Effects of Potassium. Salts on Soils ()03 

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Some Effects of Potassium Salts ox Soils 005 

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Memoir 32, The Carbon Dioxidi- of the Soil Air, the third preceding number in this series of publica- 
tions, was mailed on August 19, 1920. 



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